Strict safety requirements which are set, inter alia, by different standards apply to elevator systems. Corresponding safety guidelines are provided, in particular, by standard EN 81 (“Safety rules for the construction and installation of lifts”) from 1998 and the associated amendment A3 from 2009.
Point 12.7 of EN 81-1 relates to “Stopping the machine and checking its stopped condition”. By way of example, it is required pursuant to point 12.7.3 (“A.C. or D.C. motor supplied and controlled by static elements”) that “one of the following methods [shall] be used:
a) two independent contactors blocking the current to the motor. If, while the lift is stationary, one of the contactors has not opened the main contacts, any further movement shall be prevented, at the latest at the next change in direction of motion;
b) a system consisting of:
1. a contactor blocking the current at all poles. The coil of the contactor shall be released at least before each change in direction. If the contactor does not release, any further movement of the lift shall be prevented; and
2. a control device blocking the flow of energy in the static elements; and
3. a monitoring device to verify the blocking of the flow of energy each time the lift is stationary. If, during a normal stopping period, the blocking of the flow of energy by the static elements is not effective, the monitoring device shall cause the contactor to release and any further movement of the lift shall be prevented.”
Accordingly, it is required, in particular, that a flow of energy is blocked at each stop with a subsequent reversal in the direction of travel of a car or cage of the elevator system, that is to say that a flow of energy of a drive of the car is blocked. In addition, it is necessary to check whether the flow of energy of the drive is also actually blocked. In particular, it is necessary for the contactors to be correspondingly checked for this purpose. A stop is, in particular, intended to be understood to mean that the car reaches a stopping floor and performs an operational stop there.
Further safety requirements relate to (position) adjustment of the car. Suspension cables from which the car is suspended constitute a spring system in the event of changes in the loading of the car. Lengths of the suspension cables can change in the case of different loadings in the car. If the load in the car increases (respectively decreases), the length of the suspension cables can increase (respectively decrease).
A change of this kind in the cable length during a stop can lead to the car not being level, in the case of which the position of the car in the elevator shaft relative to the stopping floor changes. Therefore, a step may be created between the door threshold of the car and the door threshold of the shaft, that is to say a step between the floor level of the car and the level of the stopping floor.
During the course of an adjustment, the car position relative to the stopping floor is regulated or adjusted. This can be done, for example, on the basis of an absolute positioning system. Adjustment of this kind ensures, for example, that the step between the door threshold of the car and the door threshold of the shaft does not exceed a permissible limit value.
For example, point 12.12 of the standard EN 81-1 requires a stopping accuracy of ±10 mm and an adjustment accuracy of ±20 mm.
A car usually stops after a fixedly prespecified movement procedure. As soon as the car comes to a standstill at the stopping floor, the car is stopped. A service brake is activated and the flow of energy is blocked during the course of this stoppage. The contactors are accordingly released and the drive is therefore deactivated.
The situation of the car not being level specifically on account of a change in load due to people entering or exiting said car is then monitored. The car position can be determined, for example, by means of position measurement sensors for this purpose. If an unlevel position is determined, adjustment is carried out. However, in this case, a specific switch-on cycle first has to be carried out in order to reactivate the drive of the car. The contactors are initially correspondingly actuated during the course of said switch-on cycle. A drive moment or motor moment of the drive is set in accordance with a current loading of the car. The current loading of the car is determined, for example by means of a load measurement sensor, for this purpose. The drive moment is accordingly adapted during the course of pilot torque control. When the corresponding drive moment is adapted, the service brake is released and the adjustment can be carried out.
In the case of switch-on cycles of this kind, it has proven problematical to subject the drive moment to precise pilot control and setting before the service brakes are released. Particularly in the case of a large change in load of the car over a short time period (for example when a large number of passengers leave and/or enter the car), the loading of the car cannot be precisely determined or at least is hard to precisely determine using a load measurement sensor. Accordingly, the drive moment also cannot be precisely set or is at least hard to precisely set. Therefore, when the service brake is released, the car may “jerk”, that is to say the car may execute a noticeable, jerky movement.
A further problem that arises is that the adjustment can be carried out only with a certain delay. The switch-on cycle or each individual step of the switch-on cycle is accompanied by a time delay. Therefore, there is a considerable delay time between identifying the non-levelness and the adjustment being carried out. These delay times may be clearly noticed by passengers in the car and nevertheless steps can be created between the door threshold of the car and the door threshold of the shaft, these steps leading to an increased risk of tripping, even if said standard values are complied with. Elevator systems in which the service brakes are activated without the described blocking of the flow of energy during the course of stoppage of the car are also known/feasible.
Similar considerations apply to cable-free elevator systems, for example cars driven by linear drives, in an analogous manner and can be easily transferred to said cable-free elevator systems by a person skilled in the art.
Limit values for adjustment accuracy, as are required in EN 81-1 for example, usually represent a compromise between technical feasibility, according to which switch-on cycle and adjustment can be carried out, and a risk of tripping which is still acceptable in practice.
Therefore a need exists for carrying out an adjustment of a car position and blocking of a flow of energy and/or activation of a service brake of an elevator system in an improved and more efficient manner.